An automatic gearbox is a type of a vehicle transmission that automatically changes gear ratios during operation of the vehicle. Automatic transmissions have a defined set of gear ranges that are utilized in the shifting in both the upshifting and downshifting of the automatic transmission. Additionally, there are semi-automatic transmissions that allow a driver to have the option of shifting the transmission or the transmission will shift itself. Additionally, there are continuously variable transmissions (CVTs) that offer a wide range of ratios as the vehicle travels. The CVT is utilized to provide essentially an infinite number of gear ratios between a low and a high ratio. A CVT transmission, such as the one in some models of Subaru vehicles allows for the shifting by use of shift paddles associated with the steering wheel, thereby allowing the operator to shift manually from one gear to another.
Most vehicles sold in North America since the 1950s have been available with an automatic transmission. The concept is that a vehicle equipped with an automatic transmission is less complex to drive freeing the operator from the manual shifting and interaction with the clutch and the transmission shifter thereby allowing the operator to keep both hands on the steering wheel. The automatic transmission may have several operating modes that are selected by the driver, typically while the vehicle is at a standstill.
Automatic transmissions typically have several manually initiated control features, including a throttle kick-down. The throttle kick-down allows for a forced downshift in order to allow the vehicle to be mainly controlled by the engine speed in selected situations where additional acceleration is needed, such as when the operator decides to pass another vehicle. The driver can also choose between different preset shifting programs, for example, an economy mode or a performance mode. The selection of a preset shifting mode allows for either higher economy in the economy mode or delayed shifting for maximum acceleration during the performance mode. Some transmissions have a mode in which the driver has full control of the ratio changes by way of a manual selection of the ratio by way of a button or a paddle thereby overriding many of the automated features of the automatic transmission. The usefulness of such a control schema is demonstrated in such situations as in a vehicle cornering situation when a shifting of gears during the cornering operation could result in a compromise of the vehicle's balance. In the 1990s Porsche introduced a shifter that allows for the manual shifting of an otherwise automatic transmission. Additionally, some automatic transmissions, include a winter mode, such as Mercedes having a summer and winter mode that allows for the transmission to start in a gear other than first gear. When the winter selection is made the transmission will start in the second gear, rather than the first gear, to thereby reduce the tendency to lose traction.
Inputs sensors are utilized in a transmission control unit including sensors that indicate the current speed of the vehicle, a wheel speed sensor, as well as a throttle position sensor. The throttle position sensors are often utilized to determine the optimal time for selecting a gear change based on the load the engine is encountering. Additionally, the throttle position sensor can be utilized by the transmission control unit along with the vehicle speed sensor to determine the desired acceleration of the vehicle, and compare this with a nominal value, to see if the actual value is a higher or lower to thereby detect a higher load to thereby alter the characteristics of the transmission gear shift pattern. Throttle position control by the vehicle operator is the emphasis of vehicle speed control as is clear to anyone who drives a vehicle.
The problem with the speed control systems of the prior art are that the operator is utilized to provide a throttle input so that the speed of the vehicle is then regulated by the operator's continuous adjustment of the throttle input. In some instances this causes the operator to have to vary the throttle position in order to cause the transmission to shift and the operator is part of the control loop to ensure that the vehicle speed is being regulated by the throttle position maintained by the operator.
What is needed in the art is a method and apparatus to effectively control a vehicle speed based upon an operator selected speed.